Can you elaborate?
Easter and Christmas used to be pagan celebrations.
https://www.gotquestions.org/Christian-Christmas.html
For consideration.
https://www.gotquestions.org/Easter-pagan-holiday.html
The gods and goddesses of Ancient Rome became the saints and martyrs of Christianity. It was the conversation of paganism to the belief in one God.
From what I learned the early Church deliberately chose those dates for holy days.
Christmas was chosen on the first day of winter to "celebrate" the end of the darkest days of the year and the beginning of the longer-LIGHT days...the days of Jesus' life on earth.
That's what I learned. Maybe you learned differently.
Easter was paired up with Passover.